The invention relates to making an acoustic device. More particularly, the invention relates to flat plate musical instruments of the type invented in 1989 by Maurice P. Davies, now sold under the trade mark Belleplates. Such instruments and their operation are described in U.S. Pat. No. 5,177,310. This type of musical instrument is known generically as a hand plate.
The term hand plate was coined by Guy Ratcliffe in his book The Handbell Handbook, published by Mayola Music (ISBN 0-946477-02-7). As used in this specification the term hand plate defines the range of musical instruments now known by the expression.
Hand-held musical bells were known in China over 5,000 years ago. The development of handbells has been slow. It was not until the 16th century that handbells were introduced into England. Since then their popularity has grown and they are now universally rung by groups of handbell ringers.
Handbell ringers now have a choice of three types of musical instruments. The traditional bell form of handbell becomes excessively heavy when the range of notes is extended into lower octaves. This problem has been overcome in part by casting such bells from an aluminum alloy instead of the more traditional alloy of tin and copper.
Hand bells are often rung with more than one bell in each hand. This is facilitated by the open loop handles. However, the loop handle becomes impracticable as the size of the bell becomes too cumbersome or heavy to permit more than one instrument to be held in each hand.
Bell ringers also use a recently developed form of handbell known as hand chimes. These chimes consist of a tube, one end of which is bifurcated and struck externally by a clapper to cause the column of air to resonate between the bifurcated mouth of the tube and, either an optional stop plate within the tube, or, the other open end of the tube. These instruments also suffer from size and weight problems in the lower registers. The tubes become less manageable the lower the note, and such chimes have to be supported on rests whilst the clapper is caused to strike the tube.
The Belleplates described in U.S. Pat. No. 5,177,310 overcome the manageable weight and size problems of traditional bells and hand chimes. This is achieved using a light aluminum alloy, and particularly because the size of the plate between any given note and the corresponding lower octave note increases proportionally to the reciprocal of root two, that is to say, the lower note hand plate is only 1.414 times the size of the plate one octave up. As the size of hand plates increases the traditional loop handles may be replaced by a solid handle that is more durable and easily grasped for playing.
Hand plates may be played with a full five octaves (61 bells) or more. The flat shape of hand plates produces a further advantage as they may be stored and carried in a smaller space than the traditional hand bells or hand chimes.
However, hand plates need to be accurately formed to a predetermined size to produce the desired note or they have to be subsequently modified and tuned. It has been found that the structure of the clapper mechanism used on known instruments has some drawbacks and may be modified to improve the sound produced, especially when the instrument is played in the so-called plucking mode. There is a significant cost saving in the production process if the hand plates require little or no fine tuning once they have been cut to size. It has been found that the program used to operate milling machines contains a scaling facility that enables a range of hand plates to be produced using a variety of materials.
The present invention permits hand plates to be very accurately and reproducibly formed from a relatively light aluminum alloy that may be anodised or otherwise surface treated with a protective surface material.
If perfect pitch is required the hand plates may be finely tuned by the addition or removal of metal during the construction process to produce a full range of accurately tuned notes.
Hand plates produced according to the invention may be constructed with a clapper mechanism having a multi-layered striker ball or cylindrical clapper head and an adjustable bob weight on the clapper rod to achieve a variable weight effect. The offset distance between the plate and the clapper ball of the clapper mechanism may also be varied, preferably by a resilient elastomeric material that assists in the return of the clapper to its standing position. The pivot arrangement of the clapper mechanism may be modified to provide an adjustable resistance to movement.
According to the present invention there is provided a method for producing a predetermined pitch acoustic musical instrument device in the form of a hand plate comprising forming the desired shape of the hand plate from a metal sheet of known thickness and material composition by using a forming machine controlled by a programmed computer.
Preferably the forming machine is a computerised numerically controlled (CNC) milling machine, router, or a laser cutter. The computer program enables substantially identical plates to be reproduced within prescribed tolerances to provide instruments with the desired frequency and sustain characteristics. The computer program may include a spreadsheet of data required to produce the range of parameters for the desired range of instruments.
The sheet metal material of the hand plate is preferably an aluminum alloy generally selected from 2 to 5 millimeters (mm) material. The sheets may be surface treated by mechanical abrasion, such as by wire brushing, or by chemical or electrolytic etching. The surface treatment of the plates may be used to fine tune the hand plates by adding or removing material. Alternatively, the mass of the plate of a hand plate may be modified by welding on additional metal or by removing metal by milling, drilling, or the like. The thickness of sheet metal used to produce the plates may be selected to provide the desired pitch and sustain characteristics, often referred to as frequency or tone, and resonance or persistence of each note.
Hand plates produced by the above method may include a clapper mechanism consisting of a pivot means, a clapper head and a rod rigidly connecting the head to the pivot means, wherein the pivot means includes friction means for adjusting the rotational friction of a pivot axle. The friction means may be one or more screw means acting on one or both ends of the pivot axle. The adjustment provided by screw means is set to achieve the desired response for an individual ringer. The pivot axle may be rigidly connected to the rod by means of a connecting block of rigid material, such as brass or plastics. The pivot axle passes through the connecting block and may be secured to it by glue or a transverse grub screw engaging with the longitudinal side of the axle, or by an interference fit.
The clapper head may consist of a core of brass or similar hard metal material securely mounted on the end of the rod, and covered with a ball of elastomeric material that is coated with a soft felt material. The density of the soft felt material may be varied around the striking circumference of the clapper head so that, by rotation of the head on the rod a desired strike effect may be produced on the plate. A layer of woven material may replace the felt, or may be provided as an additional layer of material surrounding elastomeric ball. The ball may be spherical, cylindrical or other suitable shape for striking the plate.
An additional bob weight may be demountably mounted on the rod. The weight of the bob and the distance of the bob weight from the clapper head may also be selected and set to provide a desired effective mass of the clapper head to suit individual ringers.
At the pivot axle end of the rod a profiled and adjustable resilient cam means may be provided to bear on the plate at its acoustic node. The cam may be rotated to increase or decrease the distance of the clapper head from the plate in a standing condition. The resilience of the material of the cam may be selected to obtain the desired reaction to movement of the clapper mechanism.
In the preferred form, the method according to the present invention is applied to the production of acoustic devices as described and claimed in U.S. Pat. No. 5,177,310 (U.K. Patent 2,238,420) and as shown in U.S. Reg. Des. 339,602 (U.K. Registered Design 2,009,983).
The aluminum sheet metal for the plate may be produced by a rolling, extrusion, protrusion or pultrusion process permitting dies to produce the desired parameters of the material suitable for forming to the desired dimensions of musical instruments.